Elepaio birds (Chasiempis sandwichensis) are loyal creatures. They mate for life and dwell in the same 1- to 2-acre patch of land for their entire 15-year lives. They’re small, about five inches long, a half an ounce in weight, and quick, with the ability to change direction in midair.

Oahu elepaio.

Photo: Courtesy of Eric Vanderwerf/Pacific Rim Conservation

The bird is territorial: If an outsider elepaio crosses a pair’s imaginary white-picket fence and belts out a song, the male will deem the tune as fighting words and react aggressively, singing back, swooping over the bird or holding its long tail up at an angle.

What’s in a song? Eric VanderWerf, a wildlife biologist who has been studying birds in Hawaii since 1992, says, “Songs have well-defined purposes; the two most important are to attract a bird’s mate and to defend its territory.”

Birds also use song for species recognition, that is, to find their own kind. Endemic to the Hawaiian Islands, elepaio are separated into three subspecies, one for each island on which they’re found: Kauai (C. sandwichensis sclateri) , the Big Island (C. sandwichensis sandwichensis) and Oahu (C. sandwichensis ibidis). Although songs among each subspecies sound similar—imagine the squeak of a rubber ducky—the differences among them are apparent, once you know what to listen for.

In the mid-1990s, VanderWerf was curious if elepaio on one island would react to the songs of their counterparts on other islands. He traveled to Oahu, the Big Island, and Kauai, and placed a small speaker in the center of an elepaio territory. He played a three-minute recording from each of the three subspecies—with a rest in between—to nine birds at each site. For example, while on Kauai, he’d play the song of an Oahu elepaio bird first, a Big Island elepaio next, then one from Kauai. “The birds responded to their own island, but generally, not to the other islands. That means they don’t view those birds as potential mates or competitors, so that’s evidence that they should be considered separate species,” says VanderWerf, who published these findings in 2007.

Controlling the bird’s biggest threat, predation by non-native black rats, is VanderWerf’s current focus. “Rats will climb up a tree, find the elepaio nest, and not only eat the eggs and chicks, but, if they can, they’ll catch the female and eat her, as well,” he says.

Oahu’s elepaio are endangered, with roughly 1,500 birds left, while the other two subspecies are not. Kauai has around 40,000 to 50,000 birds and the Big Island has upwards of 100,000 birds. The difference in population numbers has to do with the birds’ second threat, diseases carried by mosquitoes, especially avian malaria and avian pox virus, neither of which are transmissible to humans. “The mosquito that carries the diseases don’t tolerate cold temperatures, so they are not found up high in the mountains,” says VanderWerf. “The majority of native birds, including elepaio, are found in higher elevations, above about 5,000 feet. On Oahu, there are no mountains that high, so there is no place that is safe from the disease.”

VanderWerf admits that although he has done research on other birds, he has an affinity for elepaio. “They have a lot of character and interesting behaviors,” he says. “And because they are declining there is a real need for information about them.”

Name That Tune

Elepaio songs are short, squeaky whistles that sound like the birds’ name, el-e-pai-o,” notes wildlife biologist Eric VanderWerf. Here’s how you can tell the three subspecies apart:

The Oahu and Hawaii elepaio songs are more similar, but the Oahu elepaio song is higher pitched.

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